During most of this century, hard gelatin capsules were a popular dosage form for prescription and over-the-counter (OTC) drugs. The ability to combine capsule halves having different colors provided manufacturers with a unique means of distinguishing various pharmaceutical products. Many patients preferred capsules over tablets, perceiving them as being easier to swallow. This consumer preference prompted pharmaceutical manufacturers to market certain products in capsule form even when they were also available in tablet form.
Generally, empty hard gelatin capsules are manufactured using automated equipment. This equipment employs rows of stainless steel pins, mounted on bars or plates, which are dipped into a gelatin solution maintained at a uniform temperature and fluidity. The pins are then withdrawn from the gelatin solution, rotated, and then inserted into drying kilns through which a strong blast of filtered air with controlled humidity is forced. A crude capsule half is thus formed over each pin during drying. Each capsule half is then stripped, trimmed to uniform length, filled and joined to an appropriate mating half.
An alternative to capsule products are caplets, which generally are solid, oblong tablets that are often coated with various polymers such as cellulose ethers to improve their aesthetics, stability, and swallowability. Typically, such polymers are applied to the tablets either from solution in organic solvents, or from aqueous dispersion via spraying. However, such spray-coated tablets lack the shiny surface and elegance of the hard gelatin capsules. Additionally, it is not commercially feasible to spray-coat a tablet with a different color coating on each end.
Another alternative to capsule products are “gelcaps,” which are elegant, shiny, consumer-preferred, dosage forms that are prepared by dipping each half of an elongated tablet in two different colors of gelatin solution. See U.S. Pat. Nos. 4,820,524; 5,538,125; 5,685,589; 5,770,225; 5,198,227; and 5,296,233, which are all incorporated by reference herein. A similar dosage form, commercially available as a “geltab,” is prepared by dipping each half of a generally round, convex tablet into different colors of gelatin solution, as described in U.S. Pat. No. 5,228,916, U.S. Pat. No. 5,436,026 and U.S. Pat. No. 5,679,406, which are all incorporated by reference herein. As used herein, such “gelcaps” and “geltabs” shall be included within the broader term, “tablets.”
However, the use of gelatin as a pharmaceutical coating material presents certain disadvantages and limitations, including the potential for decreased dissolution rate after extended storage due to cross-linking of the gelatin and potential for microbial contamination of the gelatin solution during processing. Further, the energy-related costs associated with gelatin coatings tend to be high since the gelatin material is typically applied to the substrates at an elevated temperature of at least about 40° C. in order to maintain fluidity of the gelatin, while the substrates are maintained at about 50° C. in order to minimize microbial growth.
Various attempts have been made to produce gelatin-free hard shell capsules. For example, WO 00/18835 discloses the combination of starch ethers or oxidized starch and hydrocolloids for use in preparing hard capsule shells via conventional dip molding processing. See also U.S. Pat. No. 4,001,211 (capsules prepared via pin dip coating with thermogelled methylcellulose ether compositions). However, due to potential tampering concerns, hard gelatin capsules are no longer a preferred delivery system for consumer (over-the-counter) pharmaceuticals, dietary supplements, or other such products. Additionally, the properties of an ideal composition into which steel pins are to be dipped then dried to form hard capsule shells thereon are not necessarily the same as those for dipping tablets to form a coating thereon. For example, relevant physical properties such as viscosity, weight-gain, film thickness, tensile strength, elasticity, and moisture content will differ between compositions for hard capsule formation and for coating tablets. See e.g., U.S. Pat. No. 1,787,777 (Optimal temperatures of the substrate and coating solution, residence times in the solution, and drying conditions differ.)
One disadvantage associated with dipping tablets or capsules into a non-gelatin coating system is that resulting coatings often lack adequate physical properties, e.g., tensile strength, plasticity, hardness, and thickness. Although the inclusion of plasticizers thereto may improve the plasticity properties of the coatings, such non-gelatin coating systems often disadvantageously result in tablets having soft, tacky coatings without a hardness sufficient to maintain their shape or smoothness during handling. In addition, many non-gelatin compositions do not adhere to the tablet substrate in an amount sufficient to uniformly cover the tablet after a single dipping. Further, many non-gelatin compositions lack the sufficient rheological properties necessary to maintain uniform color dispersion throughout the dipping and drying process. Attempts have been made to improve the rheological properties of these compositions by, for example, increasing their solids content in order to increase viscosity. However, such compositions often disadvantageously resulted in undesirable coating aesthetics such as surface roughness, decreased gloss, and non-uniform coating thickness.
Film forming compositions comprising hydrocolloids have been described in WO 00/18835 and WO 99/46329. However, these compositions incorporate 0.01 to 5 percent by weight of the hydrocolloids as a “setting system” in combination with known film-forming polymers such as polyvinyl alcohol, starch ethers, or oxidized starch.
One hydrocolloid, carrageenan, has been used in film coatings for pharmaceutical applications. However, carrageenan by itself was considered to be too weak for coating pharmaceutical tablets, and thus was required to be combined with microcrystalline cellulose for satisfactory coating results. See WO 00/45794. Not only is the addition of the cellulose to the carrageenan not economically advantageous, but the viscosity of the resulting mixture is also difficult to control. Moreover, the inclusion of the cellulose in such coatings tends to hinder the overall dissolution rate of the coating, which thereby delays the release time of the active contained therein.
It is desirable to find a dip coating material, which not only produces a similar elegant, shiny, high gloss, consumer-preferred dosage form similar to that of gelatin-coated forms, but which is absent the limitations of gelatin, particularly those noted above.
It is further desirable to find such a coating material suitable for use in dip coating operations, which does not inhibit the dissolution of the active coated therewith.